The long-term objective of this application is to use advances in experimental, psychometric, and statistical methods to isolate reading-related phonological processes from more general language and cognitive abilities, and to apply the results of this effort to improving (a) the early identification of children at risk for developmental dyslexia or reading disability, and (b) our understanding of causal relations between the development of phonological processes and the acquisition of beginning reading skills. There are four specific aims, two of primarily theoretical importance and two of primarily practical importance. The first specific aim is to determine how prereaders' phonological processing abilities can best be measured in general, and how phonological processing can be isolated from more general language and intellectual abilities, in particular. This will be achieved by comparing alternative modes of assessment and scoring in study one, and by combining an experimental design involving matched control tasks with advanced statistical analyses in studies two, three, and four. The second specific aim is to extend and expand a model of the nature of phonological processing abilities to prereaders. This aim will be achieved using confirmatory factor analysis to test alternative models of the nature of prereaders' phonological processing abilities in studies two, three, and four. The third specific aim is to test alternative models of developing causal relations between prereaders' phonological processing abilities and proto-literacy skills. We will achieve this aim using structural equation modeling of longitudinal data from studies three and four. The fourth and final specific aim is to determine when and how best to identify prereaders who are at risk for developmental dyslexia or reading disability. We will achieve this aim using a longitudinal predictive design in studies three and four. Success in isolating reading-related phonological processes from more general language and intellectual abilities has implications for advancing our knowledge of reading disability that extend beyond the proposed studies. Examples include providing more precise behavioral phenotypes for genetic linkage studies and more focused target and control tasks for fMRI studies.